Investigation on Protective Effect of Upper Protective Coal Seam Mining in Coal Seam Group

In the mining process of coal group B with multi outburst coal seams in Xinzhuangzi Coal Mine, the mining method from top to bottom would lead to the decrease of effective protection region layer by layer and serious loss of re-coverable resource. According to the actual layout of the roadways, three suitable positions were selected to construct boreholes to investigate the gas pressure, gas content and coal seam deformation of trend and inclination in B6 coal seam, during the mining of 66208 working face. As results, the upper and lower pressure relief angles in the tendency of B8 coal seam were determined to be 79° and 86° respectively and the pressure relief angle of direction was 75°. All three pressure relief angles are larger than the theoretical value, which indicates that the actual effective protective region is extended. After the exploitation of B8 coal seam, the permeability coefficient of B6 coal increased by 902 times compared with the original coal seam, with the gas pressure and gas content dropping to the 0.22 MPa and 2.43 m³/t, respectively. So, the effect of eliminating outburst is remarkable.